package com.bill99.util;

import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.impl.JsonWriteContext;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.SerializerProvider;
import org.codehaus.jackson.util.CharTypes;

import java.io.IOException;

public class StringUnicodeSerializer extends JsonSerializer<String> {
	
    private final char[] HEX_CHARS = "0123456789ABCDEF".toCharArray();
    private final int[] ESCAPE_CODES = CharTypes.get7BitOutputEscapes();
  
    private void writeUnicodeEscape(JsonGenerator gen, char c) throws IOException {
        gen.writeRaw('\\');
        gen.writeRaw('u');
        gen.writeRaw(HEX_CHARS[(c >> 12) & 0xF]);
        gen.writeRaw(HEX_CHARS[(c >> 8) & 0xF]);
        gen.writeRaw(HEX_CHARS[(c >> 4) & 0xF]);
        gen.writeRaw(HEX_CHARS[c & 0xF]);
    }
  
    private void writeShortEscape(JsonGenerator gen, char c) throws IOException {
        gen.writeRaw('\\');
        gen.writeRaw(c);
    }
  
    @Override
    public void serialize(String str, JsonGenerator gen,
            SerializerProvider provider) throws IOException,
            JsonProcessingException {
        int status = ((JsonWriteContext) gen.getOutputContext()).writeValue();
        switch (status) {
          case JsonWriteContext.STATUS_OK_AFTER_COLON:
            gen.writeRaw(':');
            break;
          case JsonWriteContext.STATUS_OK_AFTER_COMMA:
            gen.writeRaw(',');
            break;
          case JsonWriteContext.STATUS_EXPECT_NAME:
            throw new JsonGenerationException("Can not write string value here");
        }
        gen.writeRaw('"');//写入JSON中字符串的开头引号
        for (char c : str.toCharArray()) {
          if (c >= 0x80){
              writeUnicodeEscape(gen, c); // 为所有非ASCII字符生成转义的unicode字符
          }else {
            // 为ASCII字符中前128个字符使用转义的unicode字符  
            int code = (c < ESCAPE_CODES.length ? ESCAPE_CODES[c] : 0);
            if (code == 0){
                gen.writeRaw(c); // 此处不用转义
            }else if (code < 0){
                writeUnicodeEscape(gen, (char) (-code - 1)); // 通用转义字符
            }else {
                writeShortEscape(gen, (char) code); // 短转义字符 (\n \t ...)
            }
          }
        }
        gen.writeRaw('"');//写入JSON中字符串的结束引号 
    }
  
}
